The need for telecommunication networks capable of providing diverse and emerging communication services such as data, voice, and video motivated the development of broadband networks. Such networks offer users multimedia services, and the flexibility of accessing bandwidth on demand. Furthermore, there is increasing recognition of the benefits and advantages of using satellite transmission systems which will no doubt play a significant role in establishing a communications infrastructure for broadband communications.
The use of multimedia broadband applications in the Ka band (30/20 GHz) for satellite communication systems raises the problem of dealing with very high-speed data transmission rates, especially in the forward link segment, from satellite to the user terminals, where a broad spectrum of data is accommodated in each carrier. The main problem to overcome in a broadband communication system is how the user terminals or receivers can be made to demodulate and process the incoming high-speed data stream without requiring technology that is excessively sophisticated or expensive.
One technique that has been utilized previously to address a similar problem is an approach known as asynchronous transfer mode or ATM. ATM is based on time division multiple access (TDMA) and framing at the satellite. The satellite first buffers and then transmits the data in frames. In this approach, each frame is divided into a number of discrete time slots. Each time slot corresponds to a group of cells within the network. During each time slot, the satellite transmits to a selected group of cells. For example, if there are 7 available time slots, the cells would be divided into 7 groups. During a given time slot, the satellite would transmit data to cells in a single group. During the next time slot, the satellite would transmit to cells in a different group. This process is repeated for each frame. Therefore, during any frame, a cell would receive data in 1 time slot out of 7. By transmitting the data stream in this manner, the required data reception rates for any individual receiver within a cell can be kept at a manageable level. However, there is significant technical complexity penalty associated with the ATM approach as higher data rates are implemented.
Another approach, known as the point and shoot approach, does not involve time division or data framing at the satellite. Instead the data stream is broadcast to all associated receivers simultaneously. The signal is divided into a plurality of packets. Each packet contains addressing information identifying the intended receiver for that packet. Each receiver monitors the data stream and extracts data packets intended for that particular receiver. The primary technical challenge with this approach is designing receivers that can demodulate and process their own incoming data streams without demodulating and processing the entire broadband data stream of the information signal. Current point and shoot communication networks are capable of accommodating only relatively low data transmission/reception rates. As higher data transmission rates are required, the complexity and consequently the cost of the associated receivers needed to demodulate this high-speed data stream also increases. Since receiver products are the primary source of revenue in the satellite communications business, there is significant incentive to maintain costs of the receiver as low as possible.
Therefor, there is and continues to be a need for a practical, efficient and cost effective satellite based point and shoot type telecommunication network which is capable of conveying high-speed data streams from satellite transmitters to ground-based user terminals or receivers.